In order to measure physical properties of soils or paving materials, such as density, moisture content and compressire strength, loose samples of the soil or paving material are formed into compacted test specimens under reproducible conditions using laboratory compaction machines.
Laboratory compaction machines employing tamping as the compaction method are illustrated in U.S. Pat. No. 2,980,978 to Marshall (hereinafter the "'978 patent"). The apparatus of the '978 patent employs repetitive tamps to axially compress a sample of soil or paving material. The tamps are provided by a hamer which repetitively impacts the sample. The compaction provided by the apparatus of the '978 patent, however, is solely limited to axial compaction.
In addition compaction machines which provide axial compression while gyrating the sample of soil or paving material so as to effectively knead the sample are illustrated in U.S. Pat. Nos. 2,972,249, 3,478,572, 4,942,768 and 5,036,709 to McRae (hereinafter the "'249, '572, '768 and '709 patents", respectively) as well as a publication entitled Gyratory Shear Compacting Press By Materials des Laboratoires des Ponts et Chaussees (hereinafter the "MLPC publication"). The gyratory action, in conjunction with the axial compression of the sample, more closely simulates actual road conditions in which vehicle tires or other compaction device roll over the pavement. The McRae patents as well as the MLPC publication disclose a laboratory compaction apparatus for compressing a sample along an axis of compression while gyrating the confined sample. The gyratory effect is provided by an angular offset of the axis of compression from the central longitudinal axis of the mold which confines the sample during its gyration.
In particular, the '249 and '572 patents as well as the MLPC publication disclose a compaction apparatus utilizing a pair of oppositely disposed hydraulically actuated rams for axially compacting the sample. The use of two hydraulically actuated rams requires duplicative hydraulic systems which accordingly increases the complexity of the system as well as the likelihood of malfunctions in the hydraulic system, such as leaks in the hydraulic lines.
Furthermore, the gyrating mechanism for the compaction apparatuses disclosed by the '249 and '572 patents includes two oppositely disposed rollers mounted adjacent opposing faces of a outwardly extending flanged upper lip of the rotating mold. This gyrating mechanism and its associated drive means are mounted above the mold containing the specimen. The position of the gyratory mechanism above the mold may increase the difficulty of loading and unloading of the specimen and the mold. In addition, safety procedures must be rigidly adhered to by the operator to insure that all personnel are clear of the mold and gyratory mechanism prior to commencing compaction.